The Human Physiology Core is a state-of-the art facility for assessing in vivo human metabolism, body composition, and cardiovascular status. It provides expertise, resources, and training in: 1. Analysis of glucose, lipids, and hormones (including obesity-related hormones, e.g., leptin, adiponectin; diabetes-related hormones, e.g., insulin, C-peptide, glucagon, GLP-1, GIP; a reproductive endocrine panel; IGF-1 and its binding proteins; cytokines and markers of inflammation; isotopically-labeled glucose and amino acids by GC/MS for use in in vivo metabolic studies; isotopically-labeled water by IRMS for use in determining body composition and energy expenditure. 2. Body composition and fat distribution [(underwater weighing and BodPod for measurement of whole body density; dual-energy X ray absorptiometry (DXA) for measurement of regional and whole-body bone, fat, and soft lean tissue; magnetic resonance imaging (MRI) for body composition; isotope dilution for assessment of total body water; multi-compartment models of body composition; CT scan analysis of regional body composition (intra-abdominal and subcutaneous abdominal adipose tissue); magnetic resonance spectroscopy (MRS) for intramyocellular lipid]. 3. Insulin sensitivity testing (frequently-sampled, intravenous, glucose tolerance test with minimal modeling; euglycemic clamp); oral glucose tolerance test with analysis of insulin and glucose; mixed-meal tolerance test for determination of insulin secretion, clearance, and sensitivity. 4. In vivo glucose and protein metabolism using stable isotopes. 5. Energy expenditure (free-living energy expenditure by doubly-labeled water and isotope-ratio mass spectrometry; 24-h energy expenditure from whole-room indirect calorimetry; resting energy expenditure via indirect calorimetry), and maximal oxygen consumption via treadmill test. 6. Cardiovascular assessment (endothelial function, arterial compliance, thoracic impedance, ambulatory blood pressure, and cardiac function during exercise testing). New Methods Development includes, 1) the validation of a non-invasive test for insulin sensitivity in children using a mixed-meal, and, 2) implementation of methodology for assessing insulin secretion and clearance using data resulting from a mixed-meal test. Core services are based on the expressed needs of funded DRTC Members, and will bring together current methods in human metabolic and vascular research for application in single protocols